The present invention relates to plastic closures for use on bottles or like containers, and specifically to a plastic closure having a plurality of formations for matingly engaging corresponding ratchet formations on the container to prevent backing-off of the closure when the container and closure are in a closed position.
Molded plastic containers of the type employing a threaded closure member, such as bottles, jars, or the like normally include a smooth integral thread formed on the neck portion of the container. When a closure having a corresponding thread is tightened upon the smooth thread of the molded plastic container, there is a tendency for the closure to become loose. This loosening of the closure, commonly known as "backing-off", is due in part to vibration incurred during shipping and handling, to the self-lubricating qualities of the plastic materials normally used in molding the closures and containers, as well as to the tendency of such materials to flow or creep under stress, thereby permitting the closure to work itself off to relieve the stress set up in the threads due to tightening of the closure on the container.
Backing-off can be a significant problem to packagers, in that containers having closures which are loose or appear to have been opened are less apt to be selected by consumers for fear of tampering and/or contamination.
One suggested solution to the problem of backing-off is disclosed in U.S. Pat. No. 3,297,185, in which the lower edge margins of the threads on the container are provided with spaced depending appendages, the distal edges of which form a second load bearing surface which engages the threaded portion of a closure.
U.S. Pat. Nos. 4,345,691 and 3,924,769 disclose closures generally designed for a single use and having inwardly projecting tooth formations for engaging tooth or ratchet formations located on the neck of the closure to prevent inadvertent opening of the closure.
U.S. Pat. No. 3,977,557 discloses a two-piece container closure, the lower portion of which serves as a locking ring, and which may be provided with vertically depending auxiliary ridges which tend to bite into or engage an opposing surface in the container in such a manner as to hold the locking ring against rotation. However, the locking ring is provided in a separate piece from the actual closure itself.
A further problem with conventional container closures, especially molded plastic caps, is that the lower edge of the cap must be provided with a series of some sort of recesses to engage the lugged stripper bushing of a conventional "unscrewing" type of injection molding machinery to facilitate the removal of the cap from the mold. In applications where a molded cap is used to enclose a container having locking formations on its neck threads, such recesses may interfere with the locking action of the closure upon the container.
Thus, it is an object of the present invention to provide a back-off resistant closure for a container having laterally projecting locking formations, the closure having formations which matingly engage the locking formations of the container surface to prevent the backing-off of the closure therefrom without the use of a separate locking ring.